Evaluation of factors affecting tree and stand susceptibility to the Douglas-fir beetle (Coleoptera : Scolytidae)

Tree and site characteristics were compared between 19 groups of Douglas-fi r, Pseudotsuga menziesii (Mirb.) France (Pinaceae), infested by Douglas-fir beetle, Dendroctonus pseudotsugae Hopkins, and 19 uninfested groups to ide ntify individual or combinations of characteristics associated with Douglas -fir beetle attacks. Of the tree characteristics, diameter, height, age, ph loem thickness, bark thickness, and a standardized variable consisting of d iameter divided by the last 10 years growth rate (DBHTYG) showed significan t differences. None of the site characteristics showed significant differen ces between infested and uninfested areas. Two models, identified through d iscriminant analysis, placed 84 and 87% of the data in the correct infestat ion groups. These models included the variables diameter, height, phloem th ickness, aspect, and DBHTYG in various combinations. The results were confi rmed using a jackknifed cross-validation approach. These variables have pot ential for use in the development of a biological process model of tree and stand susceptibility to the Douglas-fir beetle.